The invention relates to a method of discrimination in spectrometry as well as to a device for implementing the method. The invention will be applicable particularly to Raman spectrometry for analysing samples, notably in the chemical industry.
At present, the analysis of samples in Raman spectrometry is a difficult operation in some cases.
As a matter of fact, the presence of fluorescent impurities in the samples is the main cause for failure in Raman spectrometry. In spite of any technical progress achieved that allowed for increasing sensitivity and in spite of the data processing of the signals that improves the signal-to-noise ratio, the detection of low intensity Raman lines can become quite difficult if they are superposed on a continuous high intensity background as encountered in phenomena of fluorescence.
The photoelectric detectors used in the visible close ultraviolet or very close infrared range have a high quantum gain and feature a very low dark current so that the predominant source of noise consists of what is generally known as "photon noise". Under these conditions, the presence of a wide spectral band of fluorescence in the spectral region where the Raman spectrum has to be observed, is the cause of significant fluctuations in photoelectric detection.
Most of the techniques proposed to remedy this situation such as frequency modulation or the subtraction of continuous background are ineffective where the "photon noise" is concerned.
At present, the only physically valid solution consists in eliminating most of the light emitted by fluorescence by using a spectroscopy technique resolved in time. This temporal discrimination technique requires the use of electronic or electrooptical picosecond "doors". Unfortunately, it is impossible to materialize them at reasonable cost and, consequently, to consider their development in the industry.